PROD UCTION OF MILK FREE FROM CONTA MINA TION 279 



carried out in the open, this danger cannot be neglected and greatly 

 reduces the value of the cooling. Cleanliness of the cooler is of 

 course essential. 



The object of cooling is to prevent the multiplication of bacteria, 

 and, when properly carried out with carefully collected milk, is of 

 great importance. The temperature of milk appears to alter slowly 

 when in bulk, whether in the direction of a rise or fall in tempera- 

 ture. An effectual preliminary cooling secures a low temperature for 

 some time afterwards. This point is well shown by the experi- 

 ments carried out by Savage. A large churn containing 17 gallons 

 of milk was employed, and four thermometers were used, the 

 bulbs being placed at different levels in the milk, as shown in the 

 figure on p. 278. 



In one case the milk was cooled in a cool chamber to about 

 4'0 C. It was then allowed to warm up gradually by being kept 

 at room temperature. The resulting temperatures are shown below. 



In another case the milk, instead of being cooled, was warmed to 

 about 55 C. The following table shows the temperatures recorded : 



